Paper Title
Antibacterial Activity of the Ethyl Acetate and Methanol Extracts of Clausena harmandiana against Bacteria Isolated from Otitis Externa Lesions of Dogs

Abstract
Aim: Otitis externa is a common disease in dogs. Although this disease has multifactorial causes, bacteria play an important role to increase the severity of the disease. In this study, we compared antibacterial activity of the ethyl acetate and methanol extracts of Clausena harmandiana root bark against bacteria isolated from otitis externa lesions of dogs. Materials and Methods: Clausena harmandiana root bark was collected and ethyl acetate and methanol extracts were prepared. Antibacterial activities of the extracts were tested using the broth microdilution method with 5 replications against 37 samples of bacteria isolated from otitis externa lesions of dogs. The isolated bacteria were 2 Gram-positive bacteria; Staphylococcus aureus, β-hemolytic Streptococcus and 4 Gram-negative bacteria; Klebsiella spp., Pseudomonas aeruginosa, Escherichia coli, and Proteus mirabilis. Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923 were also used as the standard controls. Minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were determined for two extracts. Results: Both ethyl acetate and methanol extracts have comparable MIC and MBC activity against Gram-positive bacteria. In contrast, the ethyl acetate extract showed significantly higher MIC values against Gram-negative bacteria than the methanol extract. As an overall effect of both extracts, MIC and MBC values against Gram-positive bacteria were significantly lower than that against Gram-negative bacteria. Conclusions: Both ethyl acetate and methanol extracts of Clausena harmandiana root bark have antibacterial activity against bacteria isolated from otitis externa lesions of dogs. They showed stronger inhibitory activity against Gram-positive bacteria than Gram-negative bacteria. Keywords: Clausena harmandiana, otitis externa, antibacterial activity, MIC, MBC, dogs.